When evaluating pregnant women affected with certain infectious or parasitic diseases we followed the ICD classification (WHO) (see Table 1.12), though the experts of handbooks and review papers preferred the etiological classification according to the types of agents (virus, bacterium, parasite) or the route of infections (e.g. sexually transmitted infections/diseases). However, some acute infectious diseases did not occur in the data set of the HCCSCA, though have important role in the origin of adverse pregnancy outcomes, such as spontaneous abortions (e.g. parvovirus), fetal diseases (e.g. listeriosis or again parvovirus) and birth outcomes such as PB (e.g. chlamidial infection). According to the ICD classification we had to present the data of common cold and influenza in Chapter 11, Diseases of the Respiratory System. Finally, we inserted bacterial vaginosis, vaginal candidiasis, and trichomoniasis in the Chapter 16, Diseases of Genital Organs because microbial agents were not identified in most pregnant women with vulvovaginitis-bacterial vaginosis; therefore, it seemed to be better to evaluate them together.